Concurrent eruptions at Etna, Stromboli, and Vulcano: casualty or causality?

A. Billi, R. Funiciello

Abstract

Anecdotes of concurrent eruptions at Etna, Stromboli, and Vulcano (Southern Italy) have persisted for more than
2000 years and volcanologists in recent and past times have hypothesized a causal link among these volcanoes.
Here this hypothesis is tested. To introduce the problem and provide examples of the type of expected volcanic
phenomena, narratives of the most notable examples of concurrent eruptions are provided. Then the frequency
of eruptions at each individual volcano is analysed for about the last 300 years and the expected probability of
concurrent eruptions is calculated to compare it to the observed probability. Results show that the occurrence of
concurrent eruptions is often more frequent than a random probability, particularly for the Stromboli-Vulcano
pair. These results are integrated with a statistical analysis of the earthquake catalogue to find evidence of linked
seismicity in the Etnean and Aeolian areas. Results suggest a moderate incidence of non-random concurrent
eruptions, but available data are temporally limited and do not allow an unequivocal identification of plausible
triggers; our results, however, are the first attempt to quantify a more-than-2000-years-old curious observation
and constitute a starting point for more sophisticated analyses of new data in the future. We look forward to our
prediction of a moderate incidence of concurrent eruptions being confirmed or refuted with the passage of time
and occurrence of new events.